1. Field of the Invention
The present invention relates to a power supply apparatus for electric operation which is preferably used for an electric operation apparatus.
2. Description of the Related Art
In the surgical or medical operation, an electric operation apparatus is frequently used for treatments for incising or coagulating the affected portion by applying high-frequency current.
FIG. 7 shows the structure of an electric operation apparatus 21 according to a conventional art.
The electric operation apparatus 21 comprises: a power supply apparatus 23 which receives the commercial power supply by its connection to the commercial power supply 22; high-frequency generating circuit 24 which generates a high-frequency output based on a DC power output supplied from the power supply apparatus 23; a sensor circuit 25 which detects the voltage level and the current level of the high-frequency output that is outputted from the high-frequency generating circuit 24; and a CPU circuit 26 which controls the power supply apparatus 23 and the high-frequency generating circuit 24 based on the detected result that is inputted from the sensor circuit 25.
The high-frequency output of the high-frequency generating circuit 24 is connected to a high-frequency output connector portion 27 via the sensor circuit 25, and performs the treatment such as the incision and coagulation by feeding (outputting) the high-frequency current to a high-frequency cautery treatment tool (also referred to as a high-frequency electric scalpel) connected to the high-frequency output connector portion 27.
The CPU circuit 26 outputs an output voltage instructing signal (for controlling and) for instructing the output voltage to the power supply apparatus 23 based on the detected result of the sensor circuit 25. The power supply apparatus 23 receives the output voltage instructing signal from the CPU circuit 26 and supplies, to the high-frequency generating circuit 24, the DC power output in accordance with the output voltage instructing signal. The high-frequency generating circuit 24 generates the high-frequency output based on the DC power output supplied from the power supply apparatus 23.
Hereinbelow, the structure of the conventional power supply apparatus 23 will be described.
The power supply apparatus 23 comprises: a PFC circuit (power factor improving circuit) 31; a DC/DC converter circuit 32; and a control circuit 33.
The PFC circuit 31 effectively converts, into DC power, AC power inputted from the commercial power supply 22. The DC/DC converter circuit 32 generates the DC high-voltage output (power output) in accordance with the output voltage instructing signal which is inputted from the control circuit 33, and feeds the power output from its output terminal to the high-frequency generating circuit 24.
The control circuit 33 compares the output voltage instructing signal inputted from the CPU circuit 26 with an output voltage FB signal which is obtained by feeding back an output voltage of the power output, and outputs, to the DC/DC converter circuit 32, a signal for controlling the driving the DC/DC converter circuit 32 (specifically, switching element driving signal) based on the compared signal.
FIG. 8 shows the specific structure of the control circuit 33 shown in FIG. 7 and the DC/DC converter circuit 32.
The DC/DC converter circuit 32 comprises: an FET bridge (switching element bridge) 41 having field-effect transistors (hereinafter, abbreviated to FETS) Q1 to Q4; an insulating transfer 42; a diode bridge 43; and an output smoothing filter 44.
The FET bridge 41 receives the DC power from the PFC circuit 31. The FET bridge 41 is connected to a primary wiring of the insulating transfer 42, and executes the switching operation, thereby transmitting the power to a secondary wiring.
The diode bridge 43 is connected to the secondary wiring of the insulating transfer 42, the pulsating flow shaped by the diode bridge 43 is smoothed by the output smoothing filter 44 comprising a choke coil and a condenser. The smoothed DC power output is supplied to the high-frequency generating circuit 24. A negative line in the power output is connected to a patient circuit ground (abbreviated to a patient GND in FIGS. 7 and 8).
The power output is divided to two DC voltages with proper levels via two dividing resistors Ra and Rb, then, one voltage is inputted to one input terminal of an error amplifier 45 of the control circuit 33 as an output voltage feedback signal (abbreviated to an output voltage FB signal), and another voltage is inputted to another input terminal of the error amplifier 45 as a reference output voltage instructing signal.
The error amplifier 45 outputs the compared result of both the input signals as an error amplifier output signal to a PWM control circuit (pulse width modulation control circuit) 46. The PWM control circuit 46 outputs a switching element driving signal with pulse widths varied depending on a voltage value of the error-amplifier output.
Referring to FIG. 8, the switching element driving signal is applied to gates of the FET Q1 to Q4 forming the FET bridge 41 via an insulating element 47. Consequently, the FET bridge 41 is switched (on/off).
Drains of the FET Q1 and Q2 are connected to the positive output terminal of the PFC circuit 31, and sources of the FET Q1 and Q2 are connected to drains of the FET Q3 and Q4. Sources of the FET Q3 AND Q4 are connected to a primary circuit ground (abbreviated to the primary GND in FIG. 8). The sources of the FET Q1 and Q2 are connected to both ends of the primary wiring of the insulating transfer 42, and the diode bridge 43 comprising four diodes is connected to the secondary wiring.
The operation of the control circuit 33 will be described with reference to FIG. 8. First, the output voltage instructing signal and the output voltage FB signal are inputted to the error amplifier 45. The output voltage FB signal is obtained by dividing the power output by the resistors and therefore the voltage value changes in proportion to the power output.
The error amplifier 45 compares the output voltage FB signal with the reference output voltage instructing signal, and outputs the compared result to the PWM control circuit 46.
Referring to FIG. 9, the PWM control circuit 46 includes a comparator 48 which compares the output of the error amplifier with reference zigzag waves, and outputs the compared result as a switching element driving signal.
Referring to FIG. 10, when the voltage of the reference zigzag waves are higher than the voltage of the output of the error amplifier, the PWM control circuit 46 outputs the switching element driving signal. Then, the switching element driving signal is transmitted to the FET Q1 to Q4 forming the FET bridge 41 of the DC/DC converter circuit 32 via the insulating element 47.
Under the control of the driving so as to alternately switch on/off the FET Q2 and Q3 and the FET Q1 and Q4 of the FET bridge 41 in the DC/DC converter circuit 32 by using the output of the PWM control circuit 46, the power is transmitted to the secondary wiring via the insulating transfer 42. The transmitted power is shaped by the diode bridge 43 and further the DC power output smoothed by the output smoothing filter 44 is supplied to the high-frequency generating circuit 24.
By repeating the above-mentioned control operation, the DC/DC converter circuit 32 supplies, to the high-frequency generating circuit 24, the power output in accordance with the output voltage instructing signal.
Further, referring to FIG. 8, the output smoothing filter 44 for smoothing the output voltage is arranged to the output terminal of the DC/DC converter circuit 32. The output smoothing filter 44 functions as a low path filter and therefore reduces a cut-off frequency as a capacitance Cb of a smoothing capacitor and inductance Lb of the choke coil are higher.
As the cut-off frequency of the output smoothing filter 44 is lower, noises included in the power output are reduced. On the contrary, the response speed of the power output is slow.
Incidentally, PCT international publication No. 98/07378 discloses an electric operation apparatus.